Using Copper in PCB Design & Fabrication for Maximum Reliability

Various power electronics products are being designed every day for a range of applications. Increasingly, these projects are taking advantage of a growing trend in the printed circuit board industry: heavy copper and extreme copper printed circuit boards.

What defines a heavy copper circuit? Most commercially available PCBs are manufactured for low-voltage/low-power applications, with copper traces/planes made up of copper weights ranging from 1/2oz/ft2 to 3oz/ft2. A heavy copper circuit is manufactured with copper weights anywhere from 4oz/ft2 to 20oz/ft2. Copper weights higher than 20oz/ft2, and up to 200oz/ft2 are also possible and are referred to as extreme copper. For our discussion here, we will focus primarily on heavy copper. The increased copper weight, combined with a suitable substrate and thicker plating in the through holes, can transform the once unreliable, weak circuit board into a durable and reliable wiring platform.

Sample featuring 2oz, 10oz, 20oz, and 30oz copper features on the same layer.

The construction of a heavy copper circuit endows a board with benefits such as:

Increased endurance against thermal strains

Increased current-carrying capacity

Increased mechanical strength at connector sites and in PTH holes

Use of exotic materials to their full potential (i.e., high temperature) without circuit failure

Heavy copper-plated vias carry higher current through the board and help to transfer heat to an external heat sink.

Onboard heat sinks directly plated on to the board surface using up to 120oz copper planes

Onboard high-power-density planar transformers

Although the disadvantages are few, it's important to understand the heavy copper circuit's basic construction to fully appreciate its capabilities and potential applications.

Heavy copper circuit construction
Standard printed circuit boards, whether double-sided or multilayer, are manufactured using a combination of copper etching and plating processes. Circuit layers start as thin sheets of copper foil (generally 0.5oz/ft2 to 2oz/ft2) that are etched to remove unwanted copper and plated to add copper thickness to planes, traces, pads, and plated through holes. All of the circuit layers are laminated into a complete package using an epoxy-based substrate, such as FR4 or polyimide.

Boards incorporating heavy copper circuits are produced in exactly the same way, albeit with specialized etching and plating techniques, such as high-speed/step plating and differential etching. Historically, heavy copper features were formed entirely by etching thick copper-clad laminated board material, causing uneven trace sidewalls and unacceptable undercutting. Advances in plating technology have allowed heavy copper features to be formed with a combination of plating and etching, resulting in straight sidewalls and negligible undercut.

Plating of a heavy copper circuit enables the board fabricator to increase the amount of copper thickness in plated holes and via sidewalls. It's now possible to mix heavy copper with standard features on a single board. We refer to this as PowerLink. Advantages include reduced layer count, low-impedance power distribution, smaller footprints, and potential cost savings. Normally, high-current/high-power circuits and their control circuits were produced separately on separate boards. Heavy copper plating makes it possible to integrate high-current circuits and control circuits to realize a highly dense yet simple board structure.

The heavy copper features can be seamlessly connected to standard circuits. Heavy copper and standard features can be placed with minimal restriction, provided the designer and fabricator discuss manufacturing tolerances and abilities prior to final design (see the image on the next page).

Heavy Copper circuitry is something all engineers should be considering in their design. In PTH minimum thicknes should be 1.2 mils. Heavy copper tracing can not only add strength to your traces, it also aids in convection cooling. There is obviously a higher cost involved because of higher plating times however in situations where failure is not an option, its the best way to go. We manufacture heavy copper circuits for military applications mostly as well as high voltage systems. Bottom line if you need high reliability.. go with a heavier copper. Check out www.omegacircuits.com for more info.

It is nice to have more advanced and high endurance PCBs out there, with more Ampere rating. I recall working with comercial PCBs for my final year project. The H bridges of a BLDC motor were made by us on a commercial PCB. When the load used to increase(around 16 amps) the copper wires used to melt and burn the PCB.
I hope having more powerfull PCBs will cater for higher power applications in Industries.

I definitely see the advantages of the higher current carrying capacity and improved thermal management. Copper does have a cost associated with it and I was wondering what the cost impact would be. In what situations would this technique be more cost advantageous versus using other, more conventional techniques?

The PowerLink can be defined as you described by adding an extra Gerber file such as 1A, 1B, or what ever naming convention makes sense to you. The often easier alternative is to use the fab drawing to identify areas of thicker copper. Typically these areas are obvious because the track widths are normally much larger.

In my personal experience, when designing PCBs the concern is centered around high frequency effects. This is a different realm and the artcicle is very informative. I think that one often stays away from high current becuase of the typical types of copper thicknesses that are often used.

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